Fuel cell and control unit in a detachable housing

ABSTRACT

The invention relates to a vehicle with a fuel cell for producing power. The vehicle has a monitoring and switching unit which is enclosed in a housing that is detachably connected to the fuel cell housing.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German priority document 100 06781.6, filed 18 Feb. 2000 (18.02.2000) (PCT International ApplicationNo. PCT/EP01/00879), the disclosure of which is expressly incorporatedby reference herein.

The invention relates to a fuel cell apparatus for producing electricalpower that is distributed to electrical loads in a high voltage linenetwork, and to further electrical loads in a low-voltage line networkthat is connected to the high-voltage line network via at least oneDC/DC converter. In addition to the loads, the low voltage networkcontains at least one rechargeable battery.

Mobile devices, such as vehicles with a fuel cell for producingelectrical power, often have two electrical line networks. Ahigh-voltage network, which is fed from the fuel cell, contains therelatively high-power loads, such as one or more traction motors andloads which are required for operating the vehicle when at rest or whenin motion, as well as electrical drives for auxiliary equipment forstarting and for operating the fuel cell (for example, a PEM fuel cell).The second network is a low-voltage network with relatively low-powerelectrical loads that are switched on as required during motion or whenthe mobile device is at rest. The low-voltage network is also connectedto drives and other loads, such as heating circuits or a battery, whichare required for starting the fuel cell.

The low-voltage network contains a rechargeable battery which supplieselectrical power to the appropriate loads for starting the fuel cell.Bidirectional DC/DC conversion is provided between the two networks and,during operation, supplies charging current from the fuel cell for therechargeable battery and, when required, operating current for loadsthat are connected in the low-voltage network. While one pole of thelow-voltage network is connected to the mobile apparatus ground, thehigh-voltage network is electrically isolated.

One object of the invention to provide a compact appliance which can behandled on its own and can be installed in an apparatus such that it canbe replaced.

Another object of the invention is to provide such a system that carriesout monitoring functions for electrical variables, distributionfunctions for the loads and disconnection functions in order to preventdamage in the event of critical operating states.

Still another object of the invention is to provide an arrangement forswitching functions during the phases in which the fuel cell is beingstarted and switched off, for the fuel cell, for the loads and for theline network, in the apparatus which contains a fuel cell for producingpower and contains at least one network with electrical loads that aresupplied with power from the fuel cell.

These and other objects and advantages are achieved by the apparatusaccording to the invention, which has at least one fuel cell forproducing electrical power that is distributed to electrical loads in ahigh-voltage power network connected to the fuel cell, and to furtherelectrical loads in a low-voltage power network that is connected to thehigh-voltage power network via at least one DC/DC converter, andcontains at least one rechargeable battery. A separable centralmonitoring and switching unit has a housing that can be detachablyconnected to the fuel cell housing. Conductors connected to anelectrical outputs or poles of the fuel cell are arranged via dust-tightand water-tight bushings in the wall of the housing and detachablecontact means. At least one such conductor includes a contact of a fuelcell circuit breaker in the course of the line. Branches run from theconductors, which are provided with fuses in at least one pole, todust-tight and water-tight bushings in a housing wall with detachablecontact means connected to lines from loads that are supplied with powerfrom the fuel cell. One branch from the low-voltage line network runsvia a dust and water-tight bushing to a control and evaluation unitwhich is associated with the central monitoring and switching unit andis connected to sensors for detecting the operating states of the fuelcell and of the electrical line networks. Such branch also runs via dustand water-tight bushings and easily detachable contact means in or on ahousing wall, to sensors which detect operating states of the mobileapparatus. The control and monitoring unit closes the fuel cell circuitbreaker once the fuel cell has been started and has reached itsoperational readiness. Upon detection by the sensors of the occurrenceof certain predetermined critical operating states, for which the supplyof power to the high-voltage line network must be connected ordisconnected, the control and monitoring unit opens the fuel cellcircuit breaker.

The functions which are essential for controlling and monitoring theelectrical line networks and their loads are carried out by componentsin an appliance which can be extended and can be checked separately.Fast functional testing and fault localization are thus possible. Theappliance can be manufactured at low cost as a separable unit and can beinstalled in the mobile device quickly and easily, with bushingspreventing the ingress of moisture. Operation of the appliance is thusnot adversely affected, even when located in a moist atmosphere. Asuitable control and evaluation unit is known, such as for example asdisclosed in German Patent Application 199 500 08.8. Reference is herebymade to this patent application from the same applicant.

The control and evaluation unit can be arranged in the interior of thehousing, together with the other components of the central monitoringand switching unit, and can be handled as a component of the centralmonitoring and switching unit. The other components of the monitoringand switching unit form a switching and distribution unit. In apreferred embodiment, the control and evaluation unit is arranged in itsown housing, which has the bushing for the branch for the low-voltagenetwork and the bushings for the easily detachable contact means in oron the housing wall for the line connections for the sensors fordetecting the operating states.

In one of the housing walls, plug connectors are arranged withconnections for lines that connect the control and evaluation unit tothe sensors for detecting the operating states of the fuel cell and ofthe electrical line networks. In this case, the dedicated housing can bedetachably mounted, as a cover for an opening on the housing which canbe attached to the fuel cell housing. In this embodiment, the controland evaluation unit forms a separate unit, and can be installed anddisconnected even without disconnecting the central monitoring andswitching unit. That is, this unit can also be produced, tested, storedand transported, which is advantageous, at least with regard to sparesstockholdings.

It is particularly advantageous for the housing of the control andevaluation unit to be thermally insulated from the housing with thecomponents of the switching and distribution unit. The control andevaluation unit may therefore contain electronic components whoseoperating temperature is not significantly adversely influenced by theoperating temperature of the fuel cell. For example, large-scaleintegrated electronic circuits such as processors may be provided in thecontrol and evaluation unit.

In one especially advantageous embodiment, the control and evaluationunit has a printed circuit board which is provided with electroniccomponents and is arranged in the interior of a trough-shaped cover thatcovers the housing (which is open on one side), with the components ofthe switching and distribution unit. A thermally insulating insert isprovided in front of the opening in the housing. In this embodiment,when the housing is open, both the interior of that part of themonitoring and switching unit which has the power distribution, fuse andswitching elements (that is, the switching and distribution unit) andthe control and evaluation unit in the cover are easily accessible,considerably simplifying the fuel cell system and facilitating testing,inspection and maintenance.

The apparatus is preferably designed to be mobile. In particular, theapparatus is a motor vehicle which is supplied with power from a fuelcell. However, it may also be any other mobile apparatus, such as aboat, ship, locomotive, prime mover or the like.

The water-tight bushings and the easily detachable contact means arepreferably in the form of water-tight plug connectors. The plugconnectors are secured in particular by means of “interlock” connectionsagainst being mated and disconnected while on load. These plugconnectors allow not only quick connection and disconnection of thecontacts, but also protect against the ingress of dust, water ormoisture into the housing interior.

One other option is to provide water-tight line bushings which, at leastat their ends outside the housing, have cable lugs for attachment to theassociated ends of the line networks.

In one preferred embodiment, the control and evaluation unit isconnected to gas sensors arranged outside the housing, for the detectionof leaks in units which produce hydrogen, store hydrogen or carryhydrogen, to a sensor, which is arranged in the housing with the powerdistribution, fuse and switching elements, for the fuel cell current. Itis also connected to at least one sensor arranged outside the monitoringand switching unit, for detecting an impact between the mobile deviceand an obstruction; to an arrangement situated in the housing with thepower distribution, fuse and switching elements, for measuring theinsulation resistance of the electrically insulated line network; and toa sensor which is arranged inside the monitoring and switching unit, forthe fuel cell voltage, and opens the fuel cell circuit breaker upondetection of a measured value that is undesirable or unacceptable forsafety reasons. The control and evaluation means, which are provided foroperational safety and reliability of the fuel cell system and of theline network, are protected in housings, in this embodiment. When such ameasured value such is detected, the control and evaluation unit opensthe fuel cell circuit breaker to interrupt the power output from thefuel cell, such that the line network together with the electrical loadsis changed to a safe operating state. This avoids any danger topersonnel, parts of the apparatus itself, as well as the entireapparatus with the fuel cell system and the environment. In oneparticularly expedient embodiment with a monitoring and switching unitto which a control and evaluation unit having a housing in the form of acover is connected, plug connectors which disconnect the lines to theloads when the cover is disconnected are arranged on the cover edges. Inthis case the housing, which is in the form of a cover, can be connectedby means of plug connectors to the lines to the loads. When the cover isremoved, the voltage is disconnected from the lines to the loads,provided that the loads do not include an energy store, such as abattery or a capacitor.

The control and evaluation unit monitors, in particular, the fuel celloutput current for overshooting a predeterminable limit value. It canalso monitor the current of the electrical drive and the voltages of thefuel cell and possibly monitors the low-voltage network for overshootingor undershooting predeterminable limit values and monitors theinsulation resistance for undershooting a predeterminable value.

It is expedient for the housing to be arranged at a point in the mobiledevice such that mechanical destruction of the mobile device has littleor no effect on it.

The control and evaluation unit preferably comprises integrated circuitsarranged on a printed circuit board in the housing. The conductors andbranches in the housing interior may be in the form of a cable harness,conductors using stamped grid technology, conductor tracks on a printedcircuit board (for example, a multilayer printed circuit board), copperrails, or flexible circuit technology. The nature of the conductors andbranches depends on the magnitudes of the currents which are beingdistributed. Two or more of the techniques mentioned above may also beused in the housing.

In one preferred embodiment, the fuel cell can be switched off, inparticular by detachable contacts, via a line which can be disconnectedfrom the connection to the fuel cell housing when the housing isremoved. This embodiment is a safety circuit. The safety circuit can beformed by a link via two plug contacts, or may be in the form of aseparately routed line to the high-voltage supply.

It is particularly expedient for the housing of the monitoring andswitching unit and/or the fuel cell housing to have centering or guidemeans for interlocking attachment of the housing to the fuel cellhousing. The housing can thus be fitted to the fuel cell quickly andeasily, in the position in which it is held.

The housing of the monitoring and switching unit can be screwed to thefuel cell housing, or can be attached by latching means. The mechanicalattachment of the housing to the fuel cell housing is physically simple,and can thus be produced or detached easily.

Direct attachment of the housing of the monitoring and switching unit tothe fuel cell housing results in short line sections between theelectrical outputs of the fuel cell and the fuel cell circuit breaker,which is in the form of a power switch. The joining direction of thehousing may be chosen to match the available space on the fuel cell, atan easily accessible point. The housing of the central monitoring andswitching unit can be attached to the fuel cell housing in aparticularly rigid manner. There is no need for it to be held in aparticular manner on other parts of the mobile device. The coupling ofthe housing to the fuel cell housing means that the retention of thefuel cell housing in the mobile device is sufficient for both housings,so that the housing of the monitoring and switching unit is coupled, interms of vibration and oscillations, to the fuel cell.

The nature of the attachment and the location of the housing of themonitoring and switching unit allow the housing to be fitted and removedeasily and quickly. Servicing and repair work can thus be carried outnot only with the monitoring and switching unit installed but also withit removed. The monitoring and switching unit can be installed andremoved without removal of other parts of the mobile unit.

It is expedient for a dedicated housing, or at least a compartment forfuses in the conductors and their branches, to be arranged within thehousing of the monitoring and switching unit and to be accessiblethrough a sealable opening in the housing of the monitoring andswitching unit. With this construction, fuses can be replaced easily andquickly, without having to remove the housing. The fuse holders are, inparticular, mounted on a printed circuit board. Depending on the size ofthe line cross sections of the lines running to the fuse holders, and onthe number of fuses, it is also possible to use insulated lines, stampedgrids composed of electrically highly conductive materials, conductorrails or flexible circuits with conductor tracks. The fuses for thehigh-voltage line network are preferably arranged in the fuse housing,and are accessible via an opening, which can be sealed, from outside thehousing of the monitoring and switching unit. This opening can be sealedin particular by means of the cover-like housing of the control andevaluation unit. This allows the fuses for the high-voltage line networkto be accommodated in a safe and sealed manner. The compartment with thefuses for the branches of the high-voltage network expediently has anadditional cover in the housing of the central monitoring and switchingunit. This provides safety against accidentally touching them afteropening the housing of the monitoring and switching unit.

The fuses are expediently arranged on a printed circuit board under thecover, which can be sealed, of the housing of the central monitoring andswitching unit.

The low and high-voltage line networks are DC networks, and have twopoles. Since one pole of the low-voltage line network is connected tothe mobile device ground, a single-pole fuse is sufficient for thenetwork and load lines. The branches and loads in the high-voltage linenetwork may have single-pole or two-pole protection.

The drive motor or motors for the propulsion system as well as theupstream converter and other electrical loads are protected, inparticular, in the interior of the monitoring and switching unit.

If a particularly rugged housing is required for the monitoring andswitching unit, it may be made from metal, which offers the additionaladvantage of good thermal conductivity, so that heat produced in thehousing is efficiently dissipated. The amount of heat emitted to theexterior can be increased further by means of cooling ribs or heatexchangers in some other form.

A very strong housing can also be made from a high-strength resistantplastic, which also reduces its weight. A housing such as this isexpediently composed partially of metal, if the heat is intended to bedissipated to the exterior via the highly thermally conductive metal.The housing section which is composed of metal has, in particular,cooling ribs.

In a further preferred embodiment, the housing of the monitoring andswitching unit has a switch, for example a microswitch, or sensors onhousing openings, which responds when the housing cover is opened,opening the fuel cell circuit breaker by interrupting its holdingcurrent. (The switch on the opening of the housing is arranged, forexample, in the circuit of the coil for the fuel cell circuit breaker.)Once the fuel cell circuit breaker has opened, there is no voltagewithin the housing, except for low-voltage circuits and the linesections from the outputs of the fuel cell to the contacts of the fuelcell circuit breaker. Instead of a switch on the housing cover, it isalso possible to use a sensor, for example a light barrier etc. If thecontrol and evaluation unit is arranged in the cover for the housing ofthe monitoring and switching unit, then there is no current to the fuelcell circuit breaker when the cover is removed, so that the high-voltageline network is not live.

The fuses for the low-voltage line network circuits can likewise bearranged in the housing of the monitoring and switching unit. In thiscase, they are expediently arranged so that they are accessible from theoutside and are separated from the fuses for the high-voltage linenetwork. However, it is also possible to arrange the fuse for thelow-voltage line network in an externally accessible housing, separatefrom the housing of the monitoring and switching unit. The fusedswitches are, for example, arranged on a printed circuit board. The fuseholders may also be connected to copper rails or to flexible lines or toflexible circuits with conductor tracks. An arrangement in which theconnections for the fuse holders use stamped grid technology is likewisepossible.

The fuse housing for the low-voltage line network is, by way of example,integrated in the low-voltage line network. However, a separate fusehousing is advantageous, which is externally accessible independently ofthe housing of the monitoring and switching unit.

The DC/DC converter device, which is arranged for example between thehigh and low-voltage line networks as a bidirectional converter, mayrequire a precharging current in order to start to operate. Theprecharging components may be arranged in the housing of the monitoringand switching unit. If no precharging option is required, the spacereserved for these components in the housing remains free. Anotheradvantageous arrangement for the equipment of the monitoring andswitching unit is for the components to be installed in their ownhousing, which can be fitted externally to the housing of the monitoringand switching unit, with water-tight bushings and plug connectors beingprovided for the electrical connection in the two housings.

The fuel cell circuit breaker for isolating the fuel cell from the loadsand from a hybrid battery or supercapacitor may have two poles, withboth poles being circuit breaker poles for interrupting short-circuits.However, it is also possible to design the contact for only one pole toswitch full-load and short-circuit currents. The other contact is thenonly in the form of an isolating switch, which does not have to switchhigh currents. In this case, the second contact can be opened with acertain delay with respect to the first contact, since the first contactswitches higher currents. One contact may then be a switch withoutcontacts, for example a semiconductor switch. A single-pole fuel cellcircuit breaker may also be used, which is designed for switching themaximum load current and the short-circuit current.

In order to simplify servicing and repair of components of the mobiledevice, without danger from live objects, it is expedient to provide amanually operable off switch in the housing of the monitoring andswitching unit. In this case, the off switch can be operated from theoutside without removing the housing, allowing the high-voltage linenetwork, together with its electrical loads, to be conductively isolatedfrom the fuel cell. It is expedient to provide an additional switch,which is externally accessible, for any hybrid battery or supercapacitorwhich may be used.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a fuel cell electric power distributionnetwork according to the invention;

FIG. 2 is a block diagram of a central monitoring and switching unit,which is arranged in a mobile device and is detachably connected to thefuel cell;

FIG. 3 is a perspective view of a central monitoring and switching unitwhose housing is attached to the housing of the fuel cell;

FIG. 4 is a schematic sectional view of the central monitoring andswitching unit with another housing embodiment; and

FIG. 5 is a schematic sectional view of the central monitoring andswitching unit with a further housing embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a mobile device 1, in particular a vehicle,contains a fuel cell 2, such as a PEM cell having a stack of individualfuel cell modules. The fuel cell 2 feeds electrical loads 5,6,16,17 andat least one energy store 10 such as a hybrid battery or supercapacitor,via a two-pole line network 3. Since the fuel cell 2 is formed from arelatively large number of individual modules, a higher output voltageis emitted during normal operation.

The line network 3 is therefore referred to as a high-voltage linenetwork or as a high-voltage network. The high-voltage network 3 isconnected via a converter 4 to a drive motor 5 which, for example,drives the wheels of a vehicle, and via a converter (not identified inany further detail) to a drive motor 6 for a compressor that suppliesair to the fuel cell 2. The network 3 is also connected to abidirectional DC voltage interface, for example a bidirectional DC/DCconverter 7, which has a further input/output to the vehicle powersupply network 8, whose operating voltage is lower than that of thehigh-voltage network 3. The vehicle power supply network 8 (alsoreferred to as a low-voltage network) is connected to a rechargeablebattery 9, which can be connected, for example via switches, to theDC/DC converter 7. The low-voltage network 8, whose operating voltageis, for example, 12 or 14 V, has a number of electrical loads, of whichonly a windshield wiper motor 12, a fan motor 13 and a heater 14 areillustrated in FIG. 1. A further vehicle power supply network with avoltage of 36 V or a network at 24 V for a LAN or bus may also beprovided.

The fuel cell 2 can be connected to the high-voltage line network 3 via,for example, a two-pole fuel cell circuit breaker 15. A fan motor 16 anda pump motor 17 are connected to the network 3, for example viaconverters (not identified in any more detail). Further loads (notshown) and a hybrid battery or supercapacitor 10, may also be connectedto the high-voltage network 3. The supercapacitor 10 can be disconnectedfrom the line network 3, in particular by means of an off switch 11.

The mobile apparatus 1 has a central monitoring and switching unit 18which is shown in more detail in FIG. 2. It is located in a housing 19that is detachably mounted on the housing 20 of the fuel cell 2. Thefuel cell 2 has two electrical outputs (poles) 21, 22 which areconnected to a water-tight plug connector 23. A corresponding plugconnector part 24 is located on the housing 19, and its contacts, whichare not identified in any more detail, are connected in a two-poleconfiguration via conductors 25, 26 to the contacts of an off switch 27,which can be operated by hand by means of a handle which projects out ofthe housing 19. When the off switch 27 is opened, the entirehigh-voltage network 3 located downstream from the off switch 27 isde-energized except, for example, for battery or capacitor subscriberswhich can be switched off separately so that servicing, maintenance orrepair work can be carried out on or in the mobile device, withoutremoving the housing 19 and without any danger from live parts.

Downstream from the off switch 27, the conductors 25, 26 each have amate contact 28 of a first fuel cell circuit breaker 29, and a matecontact 30 of a second fuel cell circuit breaker 31. The mate contact 28is followed by a conductor 32, and the mate contact 30 is followed by aconductor 33. The conductors 25, 36, 32 and 33 are components of thehigh-voltage network 3, which is electrically isolated. (That is, it isungrounded.) Two single-pole fuel cell circuit breakers 29, 31 improvethe disconnection safety in comparison to a two-pole fuel cell circuitbreaker with poles which are operated jointly, since the probabilitythat the two switches cannot be operated is less than the probability offailure of one switch. The off switch 27 may be omitted if precautionsare taken to ensure that the fuel cell circuit breakers 29, 31 can beoperated (disconnected) by hand.

A monitoring and switching unit 18 without a separate off-switch isshown in FIG. 1. A housing 34 with fuse holders and fuses, which will bedescribed in more detail later is located in the interior of the housing19. The conductor 32 is connected to a current sensor 35 (FIG. 2) whichhas a current transformer 36 with an annular core, through which a powerconductor is passed, without making contact. Branches 37, 38, 39, 40, 41originate from the conductor 32 downstream from the current transformer36 while branches 42, 43, 44, 45, 46 originate in a corresponding mannerfrom the conductor 33. The branches 37 to 41 run into the interior ofthe housing 34 to fuse holders having fuses, which are not identified inany more detail. Conductors run from the fuse holders of these fuses andfrom the branches 42 to 46 to a plug connector 47 in the wall of thehousing 19. Pairs 37, 42 and 38, 43; 39, 44, 40, 45 and 41, 46 formbranch lines to loads in the mobile device 1. The branch lines 37, 39,40 and 41 are provided with fuses, which are not identified in any moredetail and, together with the branch line 43 with the branches 42, 43,44, 45, 46, are intended for the connection of external lines to thehousing 18, which originate from the loads and have plug connectors 48at the ends, which correspond to the plug connector 47. The plugconnector 47 is designed to be water-tight, in the same way as the plugconnector 24. The branch lines 37, 42 and 39, 44; 40, 45; 41, 46 areconnected, for example, to the converter 4, and to the converters forthe fan and pump motors 16, 17 and for the DC/DC converter 7. Thebranches 38, 43 are connected to the drive unit, which contains aseparate protection device, by means of the converter and the drive ortraction motor 6.

The branches which are illustrated in FIG. 2 are indicated only as anexample, for illustrative purposes. There may also be more branchesdepending on the number of high-voltage loads in the mobile device.

The conductors 25, 26, 32, 33 and the branches 37 to 44 as well as theconductors which run from the fuse holders in the housing 34 to the plugconnector 47 are insulated conductors produced using stamped gridtechnology, or copper rails. Printed conductor tracks on boards orflexible circuits may also be provided. The configuration of theconductors using one of the techniques which have been mentioned dependson the number of these conductors and on the conductor cross sectionsthat are required.

The fuel cell circuit breakers 29, 31 are designed for disconnecting thefull-load current and the short-circuit current. Tripping with only asingle-pole fuel cell circuit breaker is also possible. Since the matecontacts 28, 30 must open when the fuel cell system or the vehicle is ina critical state, the provision of two contacts, which can be operatedindependently of one another, provides a higher level of confidence thatone contact will operate in the event of a defect in the other, thusdisconnecting at least one pole of the network.

The coils of the fuel cell circuit breakers 29, 31 and/or contactors orrelays are each connected to outputs of a control module in the form ofeconomizers 49 and 50, which are arranged on a printed circuit board 51in a control and evaluation unit 52, (part of the central monitoring andswitching unit 18, which will be explained in more detail later). Theeconomizers 49,50 produce a higher power for operation, that is, forpulling in, of DC contactors or relays, and then emit a lower holdingvoltage for the circuit breakers 28, 31 or relays. A relay driver module53 is also located on the printed circuit board 51, and is connected toa relay 54 which is not on the printed circuit board 51. The drivermodule 53 has two inputs, one of which is connected via a diode 55,which is arranged on the printed circuit board 51, to a plug connector56, on the housing 19, to which a key-operated switch is connected, bymeans of which the vehicle is started. When the key-operated switch isclosed, the voltage from the vehicle low-voltage network 8 is applied toone input of the driver module 53. This low-voltage network is thenormal power supply network for vehicles and contains a rechargeablebattery 9 with a voltage of, for example, 12 V, 14 V, 24 V or 36 V.Loads in this low-voltage network include, for example, windshield wipermotors, fan motors, window winder motors, lamps, indicator lights, etc.The relay 54, which is also referred to as the system relay, supplies,once it has operated, electronic components on the printed circuit board51 via its contact with the operating voltage of, for example, 12–14 V,24 V or 36 V.

There is also a further driver module 56 on the printed circuit board 51which is fitted, in particular, with the components of the control andevaluation unit 52 l. This further driver module 56 has two inputs, witha relay 57, which is not located on the printed circuit board 51 and isoutside the housing 19, being connected to its output. One conductortrack 60 on the printed circuit board 51 is connected via a plugconnector 59 in the housing 19 to the low-voltage network 8, which isconnected to the housing 19 via a plug connector (not identified in anymore detail). A number of components on the printed circuit board 51 areconnected to the conductor track 60, including the connections for theoperating power supply for the economizers 49, 50. The connection forthe operating power supply for the driver stage 53 is also connected tothe conductor track 60 via a diode, which is not identified in any moredetail. Furthermore, one connection of a power supply unit 61 isconnected to the conductor track 60. The second connection of the powersupply unit 61 is connected to vehicle ground. The power supply unit 61is in the form of a DC/DC converter and has no conductive connection (asindicated in the drawing by the transformer symbol) between the inputvoltage and the output voltage. The power supply unit 61 uses theoperating voltage of, for example, 12 or 14 V from the vehicle powersupply network to produce a higher voltage of, for example, 15 V. Therelay 57 controls precharging of the DC voltage/DC voltage interface,and has a contact 58 which is connected in parallel with one of the matecontacts 28 or 30, in series with a resistor. The coil of the relay 57is connected via a plug connector 80 to the driver module 56 and to theconductor track 60. The series-connected contact 58 and resistor 81 areconnected by means of plug connectors to lines in the housing, whichform a circuit in parallel with the mate contact 30.

The printed circuit board 51 is subdivided into two sections 63, 64 interms of the operating voltage and the voltage levels of the componentsarranged on it, thus physically isolating the components at thedifferent voltage levels. This provides a high level of safety withregard to short-circuits between components and lines, or conductortracks at different voltage levels.

Evaluation electronics 62 and a bus interface 65 (FIG. 1) are located onthe section 63 which is associated with the low voltage level. Theevaluation electronics include a logic circuit 66, which has a number ofinputs, and whose connection to components will be described in moredetail latter. On its output side, the logic circuit 66 is connected tocontrol inputs of the economizers 49, 50 and of the driver modules 53,56.

The fuel cell system has gas sensors for hydrogen, in order to monitorthe fuel. These gas sensors require operating voltages which differ fromthe voltage in the low-voltage network 8. In general, the operatingvoltage is less than the vehicle power supply network voltage. Thesignals which are produced by the gas sensors are at least not at thesame voltage level as the vehicle power supply network or in the regionof the input signals which can be processed by the logic circuit 63.Analog converter and matching circuits 67, 68 are thus provided on theprinted circuit board 51. The converter and matching circuits 67, 68each have outputs, which are not identified in any more detail, to whichthe operating voltage connections of gas sensors (not shown) areconnected via plug connectors, which are not identified in any moredetail, in the housing 19. Each converter and output circuits 67, 68also has two inputs, which are not identified in any more detail but areconnected to plug connectors in the housing 19, for the analog signalswhich are emitted from the gas sensors.

The outputs of the converter and output circuits 67, 68 are connected toone input of the logic circuit 66 and one input of a processor 69, whichis preferably a microprocessor. This input of the processor 69 may be ananalog input with a downstream A/D converter. One input of the logiccircuit 66 is designed for threshold value detection. That is, theoutput signals from the converter and matching circuits 67, 68 areprocessed further by the logic circuit 66 only if they are beyond acertain level.

The converter and matching circuits 67, 68, the logic circuit 66 and theprocessor 69 are arranged with their appropriate connections on theprinted circuit board 51 for external components and for conductortracks between the connections and the inputs of these components in thesection 63. The logic circuit 66 has further inputs, which are connectedto plug connectors 70 of the housing 19. Switching contacts, forexample, are connected to these inputs. These switching contacts areused, for example, to monitor whether devices in or on the vehicle areclosed. One switching contact 71, which is supplied with voltage fromthe vehicle power supply network 8, is provided for monitoring a coverof the housing 19. Further inputs of the logic circuit 66 are connectedvia the plug connector 70 in particular to sensors for AIRBAGS and othersensors which detect and signal collisions of the mobile device or ofthe vehicle. A further input, which is not identified in any moredetail, of the logic circuit 66 is connected to an emergency off switchvia the plug connector 70. At least one input of the logic circuit 66 isconnected to a corresponding output of the processor 69.

The processor 69 has inputs (are not identified in any greater detail)that are connected via a plug connector 72 on the housing 19 to a bus,to which other subscribers in the vehicle are also connected. The bus ispreferably the CAN bus which is known per se. A serial interface of theprocessor 69 can be connected to appropriate transmission appliances.Furthermore, the processor 69 has a BOOT input, which is not identifiedin any more detail. The reference potential for those components whichare arranged on the section 63 is the vehicle ground potential.

The current transformer 36 mounted on the section 64 is part of thecurrent sensor 35, which measures the fuel cell current using the knowncompensation principle. The current sensor 35 is connected, for example,via a multiplexer (not shown) to an A/D converter 73, which in turn isconnected by means of an optocoupler to the processor 69. Furthermore,at the output, the current sensor 35 has an optocoupler (not identifiedin any more detail) whose output is connected to one input of theprocessor 69, and to one input of the logic circuit 66. The A/Dconverter 73 is connected to one input, for example, via themultiplexer, and a line which is not illustrated is connected to thepositive output 21 or to the negative output 22.

A device 74 for measuring the isolation resistance between theelectrically isolated network and the mobile device or vehicle ground islocated in the section 64. (The isolation resistance 75 is representedby dashed lines in the drawing.) The reference potential for thosecomponents which are arranged in the section 64 is the potential of thepositive or negative output 21, 22 of the fuel cell 2. The isolationresistance 75 is measured using a known pulsed method.

During the isolation measurement, the processor 69 receives a number ofmeasured values of the voltage across the measurement resistor, onlyafter a specific waiting time, which is matched to the transient time ofthe measurement system, averages these measured values in order tominimize low-frequency interference, and then calculates the isolationresistance. During operation of the mobile device or of the vehicle,when the voltage at the output of the power supply unit 61 is available,the isolation resistance of the ungrounded network of the fuel cell 2 ismeasured continuously. In the event of unacceptable deteriorations inthe isolation, the processor 69 causes the switching contacts 28, 30 ofthe switches 29, 31 to open, via the logic circuit 66.

The current transformer 36 has an additional winding, into which adefined current is fed from a current source, in order to check theserviceability of the current transformer and the optocoupler, includingthe serviceability of the conductor tracks as far as the processor 69.

The logic circuit 66 has hardware logic functions of a combinational andsequential nature, and possibly memory functions, thus ensuring that theinput signals are processed quickly. This means that, in criticalsituations in and on the mobile device or on the vehicle, or in theevent of dangers to the vehicle occupants, which are signaled byappropriate sensors, the logic circuit 66 very quickly processes andpasses on the appropriate messages, causing the switching contacts 28,30 and 58, respectively, to open, via the economizers 49, 50 and 56,respectively. Voltage is thus removed from the high-voltage network 3together with the loads which are connected to it, so that it is nolonger possible for any danger to originate from a dangerous voltage.

The detection of a short-circuit current in the fuel cell network isreported to the processor 69 and, via the logic circuit 66, results inimmediate tripping, (opening) of the switching contacts 28, 30 and ofthe contact, if this is in the closed state.

The monitoring measures described above and the separation of theprinted circuit board 51 into a low-voltage section 63 and ahigh-voltage section 64 achieve a high level of safety on their own. Thedevice 74 for measurement of the isolation resistance is controlled oractuated from the processor 69 via an optocoupler interface, which isnot shown in any more detail. This also applies to the A/D converter 73and to the current sensor 35.

All the inputs and outputs of the components on the section 63 areresistant to short-circuits to the vehicle ground and to the 12 V, 14 Vor 24/26 V voltage and, in the event of a short-circuit, can be detectedas faults which are signaled and (in addition to signaling in the caseof short-circuits which have an unacceptable adverse effect on thesafety of operation and of the vehicle) cause the switching contacts 28,30 to be opened. The relay 57 with the contact 58 and the resistor 81 aswell as the associated conductor tracks and plug connectors are locatedin a dedicated housing 80 a, which can be detachably mounted on thehousing 19, and may be connected to the housing 19 when precharging ofcircuits and converters or transformers is required.

The low-voltage network 8 has branches of which only two are identifiedby 76, 77, in the housing 19. The branches, which have protectivedevices 78, 79 so that they are resistant to short-circuits, areconnected via plug connectors (not identified in any more detail) to acontroller 110 in the mobile device 1. The short-circuit-resistantbranches form the interface from 12–14 V to the controller 110.

All the plug connectors on the housing 19 comply at least with IngressProtection Class IP 67 in accordance with DIN 40050; that is, theyprotect against direct contact with live parts, against the ingress ofdust and against the ingress of water. Those components which arerequired for monitoring of the electrical variables relating to the fuelcell and to the line networks 3 and 8 are located on the printed circuitboard 52.

Water-tight cable bushings may also be provided, instead of the plugcontacts described above. However, plug contacts have the advantage thatthe lines can be withdrawn easily, so that the monitoring and switchingunit 16 can be removed more quickly. The components of the monitoringand switching unit 19 are designed in accordance with the motor vehiclestandard.

The housing 19 is attached to the fuel cell housing 20 by means of twocentering strips (not identified in any more detail) and screws 82, twoof which are illustrated in FIG. 2.

When the housing 19 is inserted into centering strips on the housing 20,the plug connectors 23, 24 are mated. The rigid connection between thetwo housings 19, 20 results in the central monitoring and control unit18 forming a unit which oscillates with the fuel cell 2, so that thereis no need for any dedicated mounting, that is capable of oscillation,in the mobile device 1 or in the vehicle.

The conductors 32, 33 and 37 to 44 are preferably arranged with the fuseholders on a central distribution printed circuit board in the housing19. The fuse holders together with the fuses are arranged under thecover 83 of the housing 19. (See FIG. 3.) There is also a cover on thefuses so that, when the cover is opened, the fuses and fuse holderscannot be touched until the additional cover is removed. The housing 19may be fitted in the vehicle 1 such that it can be opened fromunderneath.

The housing 19 may be composed of metal or of a resistant plastic, or ofa combination of both. The low-voltage line network 8 may have a fuseboard 84 (indicated by dashed lines in FIG. 1), in the housing 19 or atsome other point in the device 1. The arrangement in the housing 19 hasthe advantage that all the fuses are located at a central point. Thelines to the fuses for the low-voltage network 8 can be connected bymeans of plug connectors (not shown). A line 85 which loops via the fuelcell housing 20 and is passed via plug connectors between the housings19, 20 is opened when the housing 19 is removed. This line 85 isconnected to the logic circuit 66, which opens the fuel cell circuitbreakers 29, 30 when the line 85 is opened.

Plug connectors, for example 47, are arranged in the wall in the lowerpart of the housing 19. The plug connectors are connected to the wall ina dust-tight and water-tight manner. The cover 83 also covers the sidewalls of the housing and has openings in the region of the plugconnectors.

FIG. 4 shows a central monitoring and switching unit 86, which has ahousing 87 for power distribution, switching elements and fuses in thehigh-voltage line network 3 and a housing 88 which encloses the controland evaluation unit 52 that forms a part of the monitoring and switchingunit 86. Identical parts in FIGS. 1–5 are provided with the samereference symbols. The switching elements, conductor tracks, branches,and fuses on the high-voltage side of the monitoring and switching unit86 (that is, the switching and distribution unit) are identified ingeneral by 89 in FIG. 4. One face of the housing 87, which is in theform of a box, has an opening which extends entirely, or essentiallyentirely, over that face (not identified in any more detail). Thisopening can be closed off by the housing 88, which is in the form of atrough, with a U-shaped cross section. The depth of the housing 88 isintended to accommodate components of the control and evaluation unit52, whose printed circuit board 52 is arranged in the housing interior,parallel to the flat board face of the housing 88, which forms a coverfor the housing 87. The opening in the housing 89 is also covered by athermally insulating panel 90. Plug connectors 91, 92 and 93, 94,respectively, are located at the edges of the housings 87 and 88. Whenthe housings 87, 88 are connected to one another, the plug connectors 91and 93 engage in one another in the same way as the plug connectors 92and 94. The connections between the electrical components of the controland evaluation unit 51 and the electrical components of the switchingand distribution unit, which is located in that part of the monitoringand switching unit 86 which is identified as 89, run via the plugconnectors 91, 93.

The connections between the branches of the high-voltage line network 3and the loads as well as the hybrid battery and/or the supercapacitorare passed via the plug connectors 92, 94. These branch lines run withinthe housing 88 to plug connectors 95 on one side housing wall. Lineswhich are not illustrated in any more detail but are equipped withappropriate plug connectors at the ends run from the plug connectors 95to the loads and to the hybrid battery. Further plug connectors 96 onthe housing 88 are provided for connection of lines which connect thesensors described above in the mobile device to the components of theswitching and monitoring unit 52. When the housing 87 is opened byremoving the housing 88, which is in the form of a cover, the electricalconnections for the loads and for the hybrid battery are interrupted, sothat the loads are not live. There is then no longer any need to operatea special off switch. Furthermore, the control lines between theswitching and monitoring unit 52 and the battery circuit breakers areinterrupted, so that the contacts of the battery circuit breakers areopened due to the lack of the coil voltage. Both the interior of thehousing 87 and the housing 88 are then accessible, and there is no needfor a dedicated cover monitoring switch. The housing 87 is connected tothe fuel cell housing in a manner as illustrated in FIG. 3.

FIG. 5 shows a form of a housing 97, which is somewhat modified from theapparatus shown in FIG. 4 in terms of the connections, with thecomponents of the switching and distribution unit of a switching andmonitoring unit 98 and of a housing 99 for the control and evaluationunit 51, whose printed circuit board 52 is arranged within the housing99. The trough-shaped housing 99 forms the cover for the housing 97which is open on one side, since, at the lower edge, it contains plugconnectors 100 for connection of the branches to lines which run to theloads and/or to the hybrid battery or the supercapacitor.

A heat-insulating panel 103 separates the interior of the housing 97from the interior of the housing 99. Seals 104 are provided between theedges of the openings of the housings 97 and 99. On one face, which isset back with respect to the side wall of the housing 97 located aboveit, the housing 99 has plug connectors 105 for the lines to sensorsand/or signaling and indication elements, or to other bus subscribers inthe mobile device.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. Apparatus having a fuel cell for producing electrical power that isdistributed to electrical loads in a high-voltage line network connectedto the fuel cell, and to further electrical loads in a low-voltage linenetwork that is connected to the high-voltage line network via a DC/DCconverter, said apparatus further comprising: a central monitoring andswitching unit having a first housing which can be mounted detachably ona fuel cell housing of the fuel cell; electrical conductors which arearranged in said first housing and are connected to respectiveelectrical outputs of the fuel cell via contact means and bushings in awall of said first housing; wherein, at least one of said conductorsincludes a fuel cell circuit breaker; said conductors are connected toloads via branches which are provided with fuses in at least one pole,and via bushings in a wall of said first housing and contact means; thelow-voltage line network is connected via a bushing to a control andevaluation unit which is associated with the central monitoring andswitching unit; the control and evaluation unit is connected viabushings in a wall of said first housing and contact means to sensorsfor detecting operating states of the apparatus; the bushings in a wallof said first housing are dust-tight and water-tight; and the contactmeans are detachable.
 2. The apparatus according to claim 1, wherein:the control and evaluation unit closes the fuel cell circuit breakerwhen the fuel cell reaches operational readiness; and the control andevaluation unit opens the fuel cell circuit breaker upon detection ofoperating states, measured by said sensors, which correspond topredetermined critical operating states.
 3. The apparatus according toclaim 1, wherein the control and evaluation unit is arranged in aninterior of the first housing, together with the other components of thecentral monitoring and switching unit.
 4. The apparatus according toclaim 1, wherein the control and evaluation unit is arranged in a secondhousing, which is fitted as a cover for an opening in a third housingwhich encloses a switching and distribution unit for the centralmonitoring and switching unit.
 5. The apparatus according to claim 4,wherein the second housing is thermally insulated from the third housingwith the components of the switching and distribution unit for thecentral monitoring and switching unit.
 6. The apparatus according toclaim 4, wherein: the control and evaluation unit has a printed circuitboard that is fitted with electronic components and is arranged in aninterior of the second housing; and the second housing is in the form ofa trough-shaped cover and has an opening facing the opening of the thirdhousing.
 7. The apparatus according to claim 1, wherein the apparatuscomprises a motor vehicle.
 8. The apparatus according to claim 1,wherein the dust-tight and water-tight bushings and the easilydetachable contact means are plug connectors.
 9. The apparatus accordingto claim 1, wherein: the control and evaluation unit is connected to gassensors arranged outside the housing for detecting leaks in units of themobile device that produce hydrogen, store hydrogen or carry hydrogen; asensor for detecting fuel cell current; at least one sensor fordetecting an impact between the mobile apparatus and an obstruction; asensor for measuring insulation resistance of the high-voltage linenetwork; a sensor for detecting fuel cell voltage; and a sensor formeasurement of the voltage of the low-voltage line network; and thecontrol and evaluation unit opens the fuel cell circuit breaker when ameasured value is detected by any of said sensors that is undesirable orunacceptable for safety reasons.
 10. The apparatus according to claim 9,wherein the control and evaluation unit monitors: the voltages of thehigh-voltage network and of the low-voltage network to detect valueswhich exceed predeterminable limits; the fuel cell output current forovershooting a predeterminable limit; and the insulation resistance ofthe high-voltage network for undershooting a predeterminable limit. 11.The apparatus according to claim 1, wherein the first housing isarranged at a point which is substantially unaffected by mechanicaldestruction of the mobile device.
 12. The apparatus according to claim1, wherein the control and evaluation unit comprises integrated circuitswhich are arranged on a printed circuit board in the first and secondhousings.
 13. The apparatus according to claim 1, wherein the fuel cellis disconnected from the supply networks via a line which isdisconnected when the first housing is removed.
 14. The apparatusaccording to claim 1, wherein at least one of the first and secondhousings and the fuel cell housing has centering or guide means forinterlocking attachment.
 15. The apparatus according to claim 1, whereinthe first and second housings are attachable to the fuel cell housing byscrews or by latching means.
 16. The apparatus according to claim 1,wherein the first and second housings are rigidly attachable to the fuelcell housing.
 17. The apparatus according to claim 1, wherein adedicated housing for fuses in the branches is arranged in the first andsecond housings of the monitoring and switching unit.
 18. The apparatusaccording to claim 17, wherein the fuses of the high-voltage linenetwork are arranged in a fuse housing, and are accessible via acloseable opening, from outside the first housing.
 19. The apparatusaccording to claim 17, wherein the fuses are arranged on a printedcircuit board underneath a sealable cover of the first housing.
 20. Theapparatus according to claim 1, wherein the converter for a drive motorfor the mobile device is protected by a fuse in the first housing. 21.The apparatus according to claim 1, wherein the first and secondhousings are composed of metal.
 22. The apparatus according to claim 1,wherein the first and second housings are composed of plastic.
 23. Theapparatus according to claim 1, wherein the first housing comprisesmetal and plastic parts.
 24. The apparatus according to claim 1, whereinthe first housing has a switch or sensor on a housing opening, whichopens the fuel cell circuit breaker.
 25. The apparatus according toclaim 1, wherein fuses for the circuits of the low-voltage line networkare arranged in the first housing.
 26. The apparatus according to claim24, wherein fuses for the circuits of the low-voltage line network arearranged in fuse holders on a printed circuit board.
 27. The apparatusaccording to claim 1, wherein components for precharging the DC/DCconverter are arranged in a fourth housing on the first housing.
 28. Theapparatus according to claim 1, wherein a manually operable off switchis arranged in at least one of the first and second housings, upstreamof the fuel cell circuit breaker in the conductors.
 29. Apparatus fordistributing electric power from a fuel cell to loads which areconnected to a high voltage network that is connectable to the fuelcell, and to further loads in a low voltage network that is coupled tothe high voltage network, said apparatus comprising: a centralmonitoring and switching unit; a control and evaluation unit associatedwith the central monitoring and switching unit; a first housing that isdetachably mountable on a fuel cell housing of the fuel cell, saidcentral monitoring and switching unit being situated within said firsthousing; and electrical conductors which enter into said first housing,are connected at outer ends thereof to respective electrical outputs ofthe fuel cell, and are coupled at inner ends thereof to said highvoltage network; wherein said conductors are connected to said loads viaelectrical contacts and branch lines which include fuses in at least onepole thereof, and which pass through a wall of said first housing viabushings; the low voltage network is connected to said control andevaluation unit via electrical contacts and at least one bushing in awall of said first housing; the control and evaluation unit is connectedto sensors for detecting operating states of the apparatus, viaelectrical contacts and bushings in a wall of the first housing; thebushings are dust and water-tight; and the electrical contacts aredisconnectable.